1. Field of the Invention
This invention relates to magnetic recording media suitable for high density recording in which magnetic metal powders are used together with a specific type of lubricant, and a method for making such media.
2. Description of the Prior Art
In the production of magnetic recording media, it is the general practice to use metal oxides such as .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4 or CrO.sub.2 as a magnetic powder for such media. However, magnetic recording media using these magnetic metal oxide powders have not been found suitable for high density recording since they are small in coercive force and magnetic flux density. Accordingly, instead of these magnetic oxide powders, magnetic powders of metals such as Fe or Fe-Co alloys with or without other metal components have been recently used to provide high density recording media. This is because the metal powder such as Fe powder is greater in coercive force and is more convenient for high density recording. However, mere use of magnetic metal or alloy powders instead of the oxide powders presented various problems. For instance, when such metal or alloy magnetic powders are used in combination with lubricants such as stearic acid amide ordinarily employed with magnetic oxide powders, the resultant magnetic recording media show rather poor runnability or travelling performance and are liable to cause friction noise (or so-called Q noise) on contact with recording and reproducing heads or guide members. In addition, magnetic metal powders usually have a greater intensity of magnetization of particles themselves than oxide magnetic powders and thus such particles are hard to be dispersed in magnetic paint. When magnetic metal particles are mechanically treated to improve their dispersability, they tend to be broken to pieces, leading to deterioration of magnetic characteristics.
Further, it has been found that metal magnetic particles are smaller in hardness than oxide magnetic particles and become smaller in film strength when used to make a magnetic recording layer together with a binder or other constituents and tend to suffer scratches or other abrasion or wear defects on the surface thereof on application of such magnetic recording media to recording and reproducing systems as compared with oxide magnetic particles which are harder and thus less susceptible to defects on their surface.
As will be apparent from the above, the use of metal or alloy magnetic powder instead of ordinarily employed oxide magnetic powders as a magnetic powder for magnetic recording media dictates use of specific types of other constituents necessary for such media, particularly a specific type of lubricant.